CS: 1.3 Exchanging Data

Describe compression and its importance in file storage.

Compression is the process of reducing the storage space required by a file, allowing more files to be stored in the same amount of space. It is crucial for sharing files over networks or the Internet.

How does compression affect file transfer speed over the Internet?

Compressing files increases the number of files that can be transferred in a given time, making downloading a compressed file faster than downloading the full version.

Define lossy and lossless compression.

Lossy compression reduces file size by removing some information, while lossless compression reduces file size without losing any information.

Explain the difference between lossy and lossless compression with an example.

Lossy compression may result in a more pixelated image or less clear audio recording, while lossless compression allows the original file to be recovered from the compressed version.

What is Run Length Encoding (RLE) and how does it work?

Run Length Encoding is a method of lossless compression where repeated values are replaced with one occurrence of the data followed by the number of times it should be repeated.

Describe a scenario where Run Length Encoding may not offer a significant reduction in file size.

Run Length Encoding works best when there is significant repetition in the data; if there is little repetition, it may not provide a great reduction in file size.

Describe Dictionary Encoding

Dictionary encoding is a method of lossless compression where frequently occurring data is replaced with an index and stored alongside a dictionary for data restoration.

Do in Dictionary Encoding

In dictionary encoding, frequently occurring pieces of data are replaced with an index and compressed data is stored alongside a dictionary.

Define Dictionary Encoding

Dictionary encoding is a form of lossless compression where common data is replaced with an index and stored with a dictionary for data retrieval.

How does Dictionary Encoding work?

Dictionary encoding replaces frequently occurring data with an index and stores the compressed data alongside a dictionary matching data to indexes for restoration.

Describe the process of Dictionary Encoding

In Dictionary encoding, common data is replaced with an index, and the compressed data is stored with a dictionary linking data to indexes for retrieval.

Describe encryption and its purpose.

Encryption is used to keep data secure when it's being transmitted by scrambling data before transmission and deciphering it at its destination.

What is symmetric encryption and how does it work?

Symmetric encryption involves both sender and receiver sharing the same private key for encrypting and decrypting data, distributed through a key exchange process.

Explain asymmetric encryption and its key components.

Asymmetric encryption uses two keys - a public key for encrypting data and a private key for decrypting it. These keys are mathematically related and form a key pair.

How does asymmetric encryption differ from symmetric encryption in terms of key usage?

In asymmetric encryption, a public key is used for encryption and can be shared openly, while a private key is used for decryption and must be kept secret. This is unlike symmetric encryption where the same private key is used for both encryption and decryption.

Define digital signatures and how they are created using encryption keys.

Digital signatures are created using asymmetric encryption where a message is encrypted with the sender's private key. This allows anyone with the sender's public key to decrypt the message and verify its authenticity, as only the sender has access to the private key.

Describe hashing in computing.

Hashing is the process of converting an input (key) into a fixed-size value (hash) using hash functions. The output of a hash function cannot be reversed to obtain the original key.

What is a common use of hashing in storing passwords?

Hashing is useful for storing passwords as the hashed password can be checked against the key without being reversed, providing security even if the keys are compromised.

Define hash tables and their purpose.

Hash tables are data structures that store key-value pairs using a hash function and a bucket array. They allow for constant-time data lookup and are commonly used in caches and databases.

How are collisions handled in hash tables?

Collisions in hash tables occur when two keys produce the same hash. Collisions can be resolved by storing items together in a list under the hash value or by using a second hash function to generate a new hash.

Explain the characteristics of a good hash function.

A good hash function should have a low chance of collision, be quick to calculate, and produce an output smaller than the input to ensure efficient searching for the hash.

What is the significance of hash functions in comparison to encryption?

Unlike encryption, the output of a hash function cannot be reversed to obtain the original key, making it ideal for tasks like password storage where security is crucial.

How do hash tables ensure constant access times for data retrieval?

Hash tables use hash functions to determine the location in the bucket array where data is stored, allowing for constant-time data lookup regardless of the amount of data stored.

Describe a scenario where hashing is commonly used in computing.

Hashing is extensively used in situations where a large amount of data needs to be stored with constant access times, such as in caches and databases.

What is the purpose of a bucket array in a hash table?

A bucket array in a hash table is used to store data based on the hash value generated by the hash function, facilitating efficient data retrieval and storage.

How can a successful hacker benefit from gaining access to hashed passwords?

Even if a hacker gains access to hashed passwords, they cannot be reversed to obtain the original passwords, maintaining the security of user data.

Explain the role of hash functions in generating hash values.

Hash functions are algorithms that convert input keys into fixed-size hash values, ensuring data integrity and security in processes like password storage and data retrieval.

What is the impact of hash function output size on search efficiency?

A hash function should produce an output smaller than the input to ensure efficient searching for the hash, as larger outputs could lead to longer search times compared to searching for the key directly.

Describe what a relational database is

A relational database is a database that recognizes the differences between entities by creating different tables for each entity.

Define entity in the context of databases

An entity is an item of interest about which information is stored.

How are attributes related to entities in a database

Attributes are characteristics of the entity; these are categories about which data is collected.

Do flat files consist of multiple files or a single file

Flat files consist of a single file.

Describe the structure of a flat file database

A flat file database is most likely based around a single entity and its attributes, typically written as Entity1 (Attribute1, Attribute2, Attribute3 ...)

Define what a primary key is in a database

A primary key is a unique identifier for each record in the table.

How is a primary key represented in a table

The primary key is shown by underlining it.

What is a foreign key in the context of databases

A foreign key is the attribute which links two tables together.

How is a foreign key represented in a table

The foreign key is shown using an asterisk.

Describe the purpose of a secondary key in a database

A secondary key allows for quick searching in a database by setting up an index on a specific attribute, making it easier to order and search by that attribute.

Define one-to-one relationship in Entity Relationship Modelling

In a one-to-one relationship, each entity can only be linked to one other entity, like the relationship between a husband and wife.

How are one-to-many relationships represented in Entity Relationship Modelling?

One-to-many relationships are represented with a branch on one side connecting one entity to multiple other entities.

Do you need to consider redundancy when normalizing a relational database?

No, normalization aims to eliminate redundancy in a database to avoid unnecessary duplicates.

Describe the goal of normalisation in a relational database

The goal of normalization is to create the best possible layout for a database by ensuring consistent data, easy addition and removal of records, and the ability to perform complex queries.

Describe the First Normal Form in database normalization.

In First Normal Form, no attribute should contain more than a single value.

Define the Second Normal Form in database normalization.

Second Normal Form is achieved when a database in First Normal Form has no partial dependencies, meaning no attributes can depend on part of a composite key.

Explain the concept of Third Normal Form in database normalization.

Third Normal Form is reached when a database in Second Normal Form contains no non-key dependencies, ensuring that attributes only depend on the primary key.

What is the purpose of Indexing in databases?

Indexing is a method used to store the position of each record ordered by a certain attribute, facilitating quick data lookup and access.

How are primary keys handled in terms of indexing in databases?

The primary key is automatically indexed, but since it is not commonly queried, secondary keys are used for faster and easier data searching.

Describe the process of Capturing Data in a database.

Capturing data involves inputting data into the database using various methods depending on the context, such as manual entry for survey responses or scanning cheques using MICR for bank transactions.

What is Optical Mark Recognition (OMR) used for in data capture?

OMR is used for processing multiple choice questions on tests by recognizing marked choices.

Explain the importance of Selecting and Managing Data in data preprocessing.

Selecting the correct data is crucial in data preprocessing to filter out irrelevant information and manage the volume of input effectively, ensuring only relevant data is retained.

Describe the process of exchanging data using EDI (Electronic Data Interchange).

Exchanging data involves transferring collected data without human interaction, enabling data transfer between computers.

Define SQL (Structured Query Language) and its purpose.

SQL is a declarative language used to manipulate databases, allowing for creating, removing, and updating databases.

How is the SELECT statement used in SQL queries?

The SELECT statement is used to collect specific fields from a table, paired with the FROM statement to specify the table(s) the information will come from.

What is the purpose of the WHERE statement in SQL queries?

The WHERE statement is used to specify search criteria in SQL queries.

Do you need human interaction for data exchange using EDI?

No, EDI (Electronic Data Interchange) does not require human interaction for data transfer between computers.

Describe the purpose of 'ORDER BY' in SQL queries.

Specifies the order in which results should be displayed based on a specified column.

How can you sort results in descending order using 'ORDER BY' in SQL?

By adding 'Desc' to the end of the 'ORDER BY' statement.

Define 'JOIN' in SQL.

A method of combining rows from multiple tables based on a common field.

What is the common usage of 'JOIN' in SQL?

To retrieve data from multiple related tables.

Do you need a common field to perform a 'JOIN' in SQL?

Yes, a common field between the tables being joined is required.

How is a new database table created in SQL using 'CREATE'?

By using the 'CREATE TABLE' statement followed by table name and attributes.

Describe the purpose of the 'CREATE' function in SQL.

To create new databases or database objects like tables.

What does 'PRIMARY KEY' signify when creating a table in SQL?

It indicates the unique identifier for each record in the table.

Describe the details that must be specified for each attribute in a database table.

Whether it is the primary key, its data type, and whether it must be filled in ('Not Null').

Define CHAR(n) data type in a database context.

A string of fixed length n.

How is VARCHAR(n) data type different from CHAR(n) in a database?

VARCHAR(n) is a string of variable length with an upper limit of n, unlike CHAR(n) which is of fixed length.

Do you need to specify TRUE or FALSE values for a BOOLEAN data type in a database?

Yes, BOOLEAN data type requires TRUE or FALSE values.

Describe the purpose of ALTER in database management.

ALTER is used to add, delete, or modify columns in a table.

Do you need to specify the table name when adding a column using ALTER?

Yes, you need to specify the table name when adding a column using ALTER.

Define the DATE data type in a database context.

The date in the format Day/Month/Year.

How is the CURRENCY data type used in a database?

It sets the number as a monetary amount.

Describe the process of inserting a new record into a database table.

Use INSERT INTO followed by the column names and values to be inserted.

Define the TIME data type in a database context.

The time in the format Hour/Minute/Second.

Describe the UPDATE statement in SQL

It is used to update a record in a database table by setting new values for specified columns.

Provide an example of using the UPDATE statement in SQL

UPDATE TableName SET column1 = value1, column2 = value2 WHERE columnX = value

Explain the purpose of the DELETE statement in SQL

It is used to delete a record from a database table based on specified conditions.

Give an example of using the DELETE statement in SQL

DELETE FROM TableName WHERE columnX = value

Define Referential Integrity in database management

It ensures consistency by not allowing the removal of information required elsewhere in a linked database.

What is a transaction in database management?

A single operation executed on data, or sometimes a collection of operations.

What does ACID stand for in database transactions?

Atomicity, Consistency, Isolation, Durability

Explain the concept of Atomicity in ACID transactions

A transaction must be processed in its entirety or not at all.

Describe the Consistency aspect of ACID transactions

Transactions must maintain referential integrity rules between linked tables.

Explain the Isolation principle in ACID transactions

Simultaneous executions of transactions should result in the same outcome as if executed sequentially.

Define Durability in the context of ACID transactions

Once a transaction is executed, it will remain so despite external circumstances like power cuts.

What is Record Locking in database management?

It is the process of preventing simultaneous access to records to avoid inconsistencies or loss of updates.

Why is Record Locking used in databases?

To prevent multiple users from editing the same record simultaneously, ensuring data integrity.

Explain the purpose of record locking in database systems

To maintain data consistency by preventing conflicting updates to the same record.

What is the main goal of Referential Integrity in databases?

To ensure that data is not deleted if it is required by another part of the database.

How does Referential Integrity help in database management?

By enforcing constraints that prevent the deletion of data needed by other parts of the database.

Describe the concept of Transaction Processing

It involves executing single or multiple operations on data, ensuring data integrity and consistency.

Explain the importance of Transaction Processing in databases

It ensures that database operations are completed successfully and data remains accurate and reliable.

What is the significance of ACID properties in database transactions?

They guarantee that database transactions are processed reliably and consistently.

How does ACID ensure data integrity in database transactions?

By enforcing rules that maintain the correctness and reliability of data during and after transactions.

Describe deadlock in a system.

Deadlock in a system occurs when two or more processes are waiting indefinitely for an event that can only be triggered by one of the waiting processes.

Explain redundancy in data management.

Redundancy in data management involves having multiple copies of data stored in physically different locations to ensure data integrity and availability in case of damage or loss.

How does deadlock occur in a system according to the provided example?

Deadlock occurs in a system when User 1 locks Customer 1's record and tries to access Customer 2's record while User 2 locks Customer 2's record and tries to access Customer 1's record, resulting in both processes waiting indefinitely for each other's locked records.

Define redundancy in the context of data storage.

Redundancy in data storage refers to the practice of duplicating data in multiple locations to prevent data loss and ensure data recovery in case of failures or disasters.

What is the purpose of redundancy in data management?

The purpose of redundancy in data management is to safeguard important information by maintaining multiple copies of data in different physical locations to prevent data loss and ensure data availability.

Describe what a network is and its main types.

A network is two or more computers connected to transmit data. The main types are local area networks (LAN) and wide area networks (WAN).

Describe the Internet structure as a network of networks.

The Internet is a network of networks that enables global communication between computers.